The invention described herein was made by an employee of the United States Government, and may be manufactured and used by and for the Government for Government purposes without the payment of any royalties thereon of therefor.
1. Field of the Invention
The present invention relates in general to method and system for locating leaks of conductive fluid, such as ionized water, from non-conductive structures, such as pipes, as well as for detecting non-conductive structures having a conductive fluid contained or flowing therein.
2. Description of the Background Art
At present, there are a number of techniques for locating underground or hidden pipes, fluid leaks and the like. Examples of such techniques include acoustic, ultrasonic, radar and electronic signal detection methods. For example, microphones can be employed to listen for the dripping sound of a leak. Similarly, ultrasonic microphones can be used to listen for ultrasonic sounds that are generated by compressed gas leaking through very small holes in a pipe, for example. Radar can be employed to detect reflections from a buried pipe and thereby determine its location. Other pipe or leak detection methods employ systems that can detect electrical signals that are generated in the area of a pipe or a leak. For example, where a leaking fluid to be detected is conductive, such as ionized water, one known technique charges the conductive fluid to some voltage and then measures the voltage of the ground at various points until the highest voltage is found, which would be the point closest to the leak. However, this system assumes that the surrounding ground is conductive and requires actual contact with the ground to measure voltage. Other systems monitor the resistivity of the ground in the vicinity of a buried pipe, for example, to detect whether a leak has occurred. Again, such systems require actual contact of probes or the like with the ground.
All of the foregoing approaches can be time consuming and are often too expensive and/or complex for use in detecting pipes or leaks in residential environments, for example. Examples of such applications include detection of a swimming pool leak, or detection of sprinkler, watering or chilled water lines. An inexpensive alternative would be desirable for locating leaks and pipes in these and other situations where a conductive fluid is contained in or flowing inside of a non-conductive pipe or other structure.
To address the foregoing need, the present invention provides a method and system for locating leaks of conductive fluids from non-conductive structures, such as pipes, which employs a simple, inexpensive electrical signal generation and detection technique. The invention can also be used to locate non-conductive pipes or other structures themselves, where they contain a conductive fluid. The system comprises two main elements: a charge generator, such as a modulated source of voltage, which is employed to charge and discharge the conductive fluid in a time varying manner, and a capacitive type detector that can detect the variable charge that is induced in the fluid. According to the electrical theory of capacitance, as the fluid in the pipe is varied in voltage, the charged fluid induces a similar charge or voltage variation in any nearby conductors. To take advantage of this fundamental principle, the capacitive detector, which includes a large conductive pickup plate, is used to locate the pipe or leak by scanning the plate over an area where the pipe or leak is believed to be present, and detecting an induced charge that is generated when the plate comes in close proximity to the pipe or leak. However, it is important that the fluid carrying pipe not also be conductive, for if it were, the charge applied to the fluid would spread through the pipe into the surrounding ground, thus preventing the requisite charging of the fluid.
In a preferred embodiment, the charge generator is a function generator that is set to ramp through a set of variable voltage low frequency audio signals about once or twice a second and thereby generates a series of xe2x80x9cchirps.xe2x80x9d The resulting signal is applied to the fluid in the pipe, whose location is to be detected, by connecting the output of the function generator via an electrical line to a spigot or fitting, or by dropping the electrical line into the fluid at any suitable accessible location. The varying voltage of the chirped signal charges and discharges the fluid in the pipe, which can be detected by the pickup plate in the detector if the plate is held in close proximity, e.g., within 10 feet, to the pipe. In addition, if a leak is encountered, the resulting signal will appear over an area larger than expected for a buried pipe, assuming the leak provides an electrically conductive path between the flow and the wet surrounding ground.
The detector is preferably a handheld device that is designed much like a conventional metal detector, for example, and can be used to scan the ground or other area for a buried pipe, leak or other structure. In the detector, the charge induced on the pickup plate by the varying charge in the fluid is preferably amplified and then used to actuate any suitable type of indicator device, such as pair of headphones that enable an operator to hear the modulated signal as a chirping sound, for example.
The primary application of the invention is for locating water leaks in commercial, residential and industrial settings where PVC, which, is electrically insulating, is being used as the pipe material, as well as for locating the PVC pipes themselves. However, the invention can be used with any type of electrically insulating pipe material. It should also be noted that while pure water is not conductive, in the vast majority of cases compounds are added to water, which ionizes it and makes it sufficiently conductive for the invention to work. The invention allows a user to trace the location of buried pipes containing a conductive substance such as water over distances of potentially two or three hundred feet from the point at which the signal is applied to the fluid.